Electronically controlled artificial intervertebral disc with motor assisted actuation systems

ABSTRACT

An electronically assisted artificial vertebral disc having an upper disc plate and a lower disc plate is disclosed. An actuator imparts movement to at least one of the upper and lower disc plates. A control device controls the actuator and the amount of movement between the disc plates. The actuator includes a plurality of either linear actuators or rotary actuators that are driven by electric motors in response to the control device. The control device includes at least a first sensor for detecting the position of the actuator and at least a second sensor for detecting the spatial orientation of at least one of the upper and lower disc plates. The control device also preferably includes a microprocessor that calculates the desired positions of the upper and lower disc plates and provides a control signal to the actuator to drive the upper and lower disc plates to their desired positions.

This application claims priority under 35 U.S.C. §119(e) of U.S.provisional application No. 60/793,329, filed on Apr. 20, 2006, theentire contents of which are hereby incorporated by reference.

BACKGROUND OF INVENTION

1. Field of the Invention

The present invention relates to surgically implantable artificial discsand more specifically to electro-mechanical intervertebral discs(“EMDs”).

2. Description of the Relevant Art

Spinal pain secondary to degenerative disc disease is a major source ofdisability. When conservative medical treatment fails to amelioratedisabling symptoms, a variety of surgical solutions are available. Thesesolutions include percutaneous or open surgical discectomies, fusionsand more recently, placement of prosthetic discs. Typically thesetreatments lead to either rigid or semi constrained motion of the discspace.

The history of artificial disc embodiments and their surgicalapplications in the entire spine has been thoroughly reviewed in ourissued U.S. Pat. No. 7,083,650 and our two pending patent applicationSer. No. 11/684,787 and Ser. No. 11/536,815 which are incorporatedherein by reference. The history of spinal fusion embodiments and theirsurgical applications in the entire spine is thoroughly reviewed in ourissued patent and pending patent applications.

Currently no available prosthetic spinal disc truly simulates naturaldisc function in that there are more or less static responses of theimplant to changing axial loading forces. The young healthy hydratednatural disc with its viscoelastic nucleus pulposus has the naturalability to sense linear and angular degrees of motion and respond bychanging volumetric shape due to different axial loading forces. Upondehydration the capacity for dynamic expansion is lost. This amongstother changes may lead to pain generation.

Current embodiments of artificial discs have different degrees ofsuccess by replacing and expanding disc heights in a static non-dynamicmanner. There are currently no known implantable systems which canconstantly sense movements and dynamically respond to the entirespectrum of continuous and variable kinematic and gravitational forces,and effect a motor response by modulating natural or artificial discvolume/height.

A recent published U.S. Patent Application 20050273170, by Navarro etal., describes the incorporation of a microprocessor into an artificialdisc. This microprocessor stores information which enables surgeons tomoderate patients' activities during the post operative period afterimplantation of an artificial disc. This device, however, does not havethe capabilities of dynamically responding to real time sensoryinformation which can be transmitted real-time to screw motors and henceconstantly modulate disc height, volume, angle and degrees of motion viahighly tuned motor outputs in response to sensory inputs. Furthermorethis device is not based on linear activation systems or rotary motoractuators.

U.S. Patent Publication 20040177531, entitled “Intelligent footwearsystems”, by DiBenedetto et. al., describes an intelligent system forarticles of footwear that adjust automatically in response to measuredperformance characteristics utilizing sensors and motors. This type ofmodulatory system has hitherto not been incorporated into any artificialdisc or joint.

In our previous patent applications identified above, we presentedmultiple embodiments of safely implantable spinal artificial discs. Inthe present application, we disclose an advance to our prior patenteddesigns, and this advance is intended to treat and restore early andlate degenerative discs by implanting an intelligent system which candynamically sense, respond and regulate disc motion. This more closelysimulates natural disc function, and thereby has the capacity to furtherimprove the quality of life of patients with painful degenerative discdisease.

SUMMARY OF THE INVENTION

A surgically implantable artificial disc and a method for implantingsuch a disc are disclosed. More specifically, various electro-mechanicalintervertebral discs (EMDs) are disclosed. The first two embodiments arebased on linear actuation systems (LASs) comprised of axially orientedtelescoping cylinders coupled with position and motion sensors thatfeed-back via a microchip to an internalized lead screw motor, therebydynamically altering the height and angle of the intervertebral disc.The third and fourth embodiments employ rotary motors to actuateflexion, extension, rotation and lateral bending. These electronicallycontrolled artificial intervertebral discs (ECAIDs) respond with greatsensitivity to the full spectrum of human locomotor activities, and to360 degrees of spinal motion. This leads to exquisitely modified dynamicdisc motion in response to differing spinal positions and locomotoractivity thereby accurately simulating natural spinal disc function.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates an electronically assisted artificial disc with aball/trough design, microchip, and three linear activation systems(“LASs”) (Embodiment I).

FIG. 2 illustrates a control algorithm of the electro-mechanicalartificial disc (Embodiments I, II, and II).

FIGS. 3A (1)-(4) illustrates the LAS components of theelectro-mechanical artificial disc (Embodiment I).

FIG. 3B illustrates the inner aspect of the EMD superior plate(Embodiment I).

FIG. 3C illustrates the inner aspect of the EMD inferior plate(Embodiment I).

FIG. 4 illustrates a three-dimensional view of an EMD (Embodiment II).

FIG. 5A illustrates the superior disc plate of the EMD (Embodiment II)

FIG. 5B illustrates the inferior disc plate of the EMD (Embodiment II).

FIG. 6A illustrates an exploded view of the EMD, Roller-Bearing design(Embodiment III).

FIG. 6B illustrates a lateral view of the EMD, Roller-Bearing design(Embodiment III).

FIG. 6C illustrates a perspective view of the EMD, Roller-Bearing design(Embodiment III).

FIG. 7A illustrates the inferior aspect of the superior plate withguidance ring of EMD, Roller-Bearing design (Embodiment III).

FIG. 7B illustrates the intermeshing of the guidance ring with gearmotors of the EMD, Roller-Bearing design (Embodiment III).

FIG. 7C illustrates the superior view of the Roller found in the EMD(Embodiment III).

FIG. 7D illustrates the inferior view of the Roller found in the EMD(Embodiment III).

FIG. 7E illustrates the superior view of the inferior plate of the EMD(Embodiment III).

FIG. 8 illustrates a three-dimensional view of an Electromechanical Disc(EMD), Roller-Bearing design with a position-force sensor (EmbodimentIV).

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The Medical Device

Referring now to FIGS. 1-3, the above described problem can be solved bythe surgical implantation of an artificial intervertebral disc 100. Anexemplary embodiment of an electronically assisted artificial vertebraldisc 100 comprises an upper disc plate 104, a lower disc plate 103disposed beneath the upper disc plate 104, an actuator (e.g.105) forimparting movement to at least one of the upper 104 and lower 103 discplates; and a control device (e.g., 301) for controlling the actuator(e.g., 105) and the amount of movement between the disc plates 104, 103.The disc plates 104, 103 can include anchoring spikes 113. Theartificial intervertebral disc 100 includes a ball 101 and trough 102,with three linear activation systems (hereinafter “LASs”) 105 placedcircumferentially around the core ball/trough. The LASs 105 are eachcomprised of two universal joints 106, two struts 107 surrounding amotor-controlled lead screw 109 (FIGS. 1 and 3A). The motor assembly 108for the lead-screw 109 in the LAS 105 is illustrated in FIG. 3A(4). Thisfigure also illustrates how rotation within the motor assembly 108effects linear motion in the struts 107. The stator 111 causes rotationsin the rotor 110 thereby rotating the lead screw 109 which then causesthe strut 107 to engage or disengage. In order to assess the degree ofengagement or disengagement of the strut 107 from the lead screw 109 arotation sensor 112 signals the number of turns completed by the leadscrew 109. This data is processed to calculate the total change inheight of the strut motor system. FIG. 3B illustrates the inner aspectof the artificial disc shell (e.g., artificial disc plate 104). Itillustrates the hermetically sealed control circuit (microchip) 301, thegyroscopic sensor 302, slots 303 for the universal joints 106, positionsensors 305 and electrical conduits 306. FIG. 3C illustrates the inneraspect of the opposing artificial disc plate 103 comprised of the trough102 and slots 303 for the universal joints 106. The trough 102 includesa plurality of channels 307 on a circumferential surface thereof, thecircumferential surface extending in a direction away from the one ofthe upper disc plate and the lower disc plate. Each of the plurality ofchannels 307 corresponds to one of the slots 303.

FIG. 2 illustrates the control algorithm of the electro-mechanicalartificial disc as it cycles. The gyroscopic sensor 302 obtainsmacroscopic (i.e. full body) speed, orientation and velocity. Such agyroscopic sensor may be of a type described in ADXL330 Specifications,“Small, low power, 3-Axis±3 g iMEMS accelerometer” ADXL330, AnalogDevices, Inc., Norwood Mass., 2006. This in turn estimates motion e.g.walking, running, lifting, swimming etc. and is mapped as described inV. Feipel, T. De Mesmaeker, P. Klein, M. Rooze, “Three-dimensionalkinematics of the lumbar spine during treadmill walking at differentspeeds”, Eur. Spine J 10: 16-22, 2001, in order to find a desiredposition/trajectory of the disc plates. The universal joint 106 and leadscrew sensors 305 obtain positions of the opposing plates 101, 102relative to each other. The lead screw sensors 305 may be of a typedescribed in R. Pallas-Areny, J. G. Webster, Sensors and SignalConditioning, 2^(nd) Ed., John Wiley & Sons, NY, 2001. This data iscompared with a desired position/trajectory in the microchip 301, andfuture position of the top-plate 102 is thereby determined from thedifference between current and desired positions. The lead screws 109are then correspondingly adjusted to obtain this desired position in theLAS 105. The subsequent cycle (N+1) repeats ad infinitum at a frequencythat supersedes, and is relatively much higher than, the change ofmacroscopic motion in the spine. The battery which can be replaceable orrechargeable is implanted percutaneously under the skin where it iseasily accessible. It is also hermetically sealed.

FIG. 4 illustrates a complete electronically controlled disc 400 havingplates 401 and 402 (Embodiment II). This does not have a ball andtrough. Instead it has six LASs 105 that form a Stewart-type platform ofthe type described in N. Smith and J. Wendlandt, “Creating a Stewartplatform model using SimMechanics”, Newsletter—MATLAB Digest, TheMathWorks, Inc, Natick Mass., September 2002. See also D. Stewart, “Aplatform with six degrees of freedom” Proceedings of The Institution ofMechanical Engineers, 180 Part 1, No. 15, pp. 371-386, 1965-66. Thestructure and function of the LASs 105 is identical to Embodiment I.FIGS. 5A and 5B illustrate the LAS slot configurations for the opposingartificial disc plates 401, 402.

FIGS. 6 and 7 illustrate the electromechanical disc (EMD) 600,Roller-Bearing design (Embodiment III). We will now describe themechanism of sensory-motor coupling and actuation for the EMD 600,Embodiment III. This EMD 600 has superior and inferior plates 601, 602which are each uniquely designed (FIGS. 6A-C, and FIGS. 7A-7E.). Theinferior plate 602 provides motor housing 603 and a flexion/extensionrotation motor shaft bearing 701 (FIG. 7E) for the shaft 620 of theroller 605 (FIG. 7D), and also has embedded motor and torque sensors 607which sense the force with which the roller 605 rotates against theinferior plate 602 (FIGS. 6A-C). Additionally it can sense the positionthat the roller 605 is in.

The inferior plate 602 magnetically controls the shaft 620 and henceposition of the roller 605. The position of the roller 605 determinesthe degree of flexion and extension exhibited by the patient.

Within the roller 605 are embedded motor and sensor 607 pair respondingto spatial rotation (FIG. 6A). The sensor 607 detects the rotationalposition of the superior plate 601, and detects the velocity of thepatient. Subsequent to this information being processed, the adjacentmotor is activated initiating further rotation consistent with thepredicted or anticipated motion of the superior and inferior vertebralbodies. A regenerative energy conserving power source can beincorporated into the roller 605.

The gear mesh which consists of the guidance ring 609 with two gearedmotors 611, 612, one of which behaves as a sensor, (FIGS. 6A, 7A and 7B)is responsible for a vertebral rotation feed-back loop. The guidancering 609 is fixed in the superior plate 601, (FIG. 7A) thereforerotation of the superior vertebral body precisely determines therotation of the guidance ring 609. The guidance ring 609 thereby effectsa gear motor that is acting as a sensor in its passive state (FIG. 7B).Within milliseconds the other gear motor initiates a proportionaterotation, thereby rotating the guidance ring 609, and the uppervertebral body.

FIG. 7C illustrates that the shaft of the geared motors 611, 612 isinserted into the motor gear interface 613. The guidance ring bearings614 serve as a bearing for the guidance ring 609.

FIG. 8 illustrates a fourth EMD embodiment 800 which is based on aRoller-Bearing design as in Embodiment III. However, in addition toEmbodiment III, it also contains a position and force sensor system 804.In Embodiment IV the superior disc plate 801 is rigidly attached to acurved protruding element 803. Correspondingly the inferior disc plate802 is rigidly attached to a curved slot element 805. The protrudingelement 803 has the ability to rotate within the slot element 805 aswell as to translate along the slot element 805. The slot element 805will sense the acceleration and position of the protruding element 803,and thereby obtain the force and position experienced by the superiorand inferior disc plates 801, 802.

Surgical Approach

The surgical implantation of embodiments I, II, III and IV is identicalto the techniques described in our previous patent and patentapplications, U.S. Pat. No. 7,083,650 and pending patent applicationSer. No. 11/684,787 and Ser. No. 11/536,815. In addition, afterimplantation, the insulated leads are brought to the dorsal surface,attached to the comptroller power complex which is buried subcutaneouslyallowing battery access (not illustrated).

The current embodiments for placement of ECAIDs further enhanceprosthetic disc function by more closely simulating the natural discfunction by dynamically responding to changes in locomotion and spinalmotion gradients hence making it a more effective disc substitute whichprovides constant real-time dynamic changes.

These embodiments have the potential to lead to significant advances inthe care of the spinal patient. Furthermore it is possible that thistechnology in the future may be applicable to other early diseasedjoints in the body.

The invention has been described with reference to exemplaryembodiments. However, it will be readily apparent to those skilled inthe art that it is possible to embody the invention in specific formsother than those of the embodiments described above. This may be donewithout departing from the sprit of the invention. The exemplaryembodiments are merely illustrative and should not be consideredrestrictive in any way. The scope of the invention is given by theappended claims, rather than the preceding description, and allvariations and equivalents which fall within the range of the claims areintended to be embraced therein.

1. An electronically assisted artificial vertebral disc, comprising: an upper disc plate; a lower disc plate disposed beneath the upper disc plate; a mechanism for allowing relative motion between the upper disc plate and the lower disc plate, wherein the mechanism for allowing relative movement includes a ball on one of the upper disc plate and the lower disc plate, and a trough on another of the upper disc plate and the lower disc plate; an actuator for imparting movement to at least one of the upper disc plate and the lower disc plate; and a control device that continuously controls the actuator and an amount of movement between the upper disc plate and the lower disc plate, wherein the actuator includes a plurality of linear actuators interposing the upper disc plate and the lower disc plate, each of the linear actuators including a first end coupled to the upper disc plate and a second end coupled to the lower disc plate at positions circumferentially surrounding the ball and the trough.
 2. The electronically assisted artificial vertebral disc according to claim 1, wherein each of the plurality of linear actuators is driven by an electric motor which is responsive to the control device.
 3. The electronically assisted artificial vertebral disc according to claim 2, wherein each of the plurality of linear actuators includes: universal joints that connect to the lower and upper disc plates; at least one strut connected to the universal joints; a lead screw disposed within the at least one strut; and an electric motor for rotating the lead screw and causing relative movement between the upper and lower disc plates.
 4. The electronically assisted artificial vertebral disc according to claim 3, wherein the upper and lower disc plates include anchoring spikes.
 5. The electronically assisted artificial vertebral disc according to claim 2, wherein the control device includes: at least a first sensor for detecting the position of the actuator; at least a second sensor for detecting a spatial orientation of at least one of the upper and lower disc plates; and a microprocessor that calculates desired positions of the upper and lower disc plates and provides a control signal to the actuator to drive the upper and lower disc plates to their desired positions.
 6. The electronically assisted artificial vertebral disc according to claim 5, wherein the second sensor includes a gyroscopic sensor.
 7. The electronically assisted artificial vertebral disc of claim 2, wherein each of the plurality of linear actuators includes: a strut body; a first universal joint coupling a first end of the strut body to the upper disc plate; a second universal joint coupling a second end of the strut body to the lower disc plate; a lead screw movably disposed within the strut body, an electric motor coupled to the lead screw and responsive to the control device, the electric motor selectively rotating the lead screw in response to the control device and causing relative movement the upper disc plate one of away from and toward the lower disc plate.
 8. The electronically assisted artificial vertebral disc of claim 7, wherein the strut body includes a first strut portion aligned axially with a second strut portion, wherein the lead screw interposes the first strut portion and the second strut portion and is rotatably engaged with at least one of the first strut portion and the second strut portion, wherein rotation of the lead screw in a first direction by the electric motor linearly moves the first strut portion in an axial direction away from the second strut portion, and wherein rotation of the lead screw in a second direction by the electric motor linearly moves the first strut portion in an axial direction toward the second strut portion.
 9. The electronically assisted artificial vertebral disc of claim 8, wherein the electric motor includes: a stator coupled to the lead screw; and a rotor coupled to the stator.
 10. The electronically assisted artificial vertebral disc of claim 9, comprising: a first sensor that detects a rotational position of the stator.
 11. The electronically assisted artificial vertebral disc of claim 9, wherein the control device includes: a plurality of first sensors, each of the plurality of first sensors coupled to the stator of each of the plurality of linear actuators and detecting a position of each of the plurality of linear actuators based on a rotational position of the stator, a second sensor coupled to one of the upper disc plate and the lower disc plate, the second sensor detecting a spatial orientation of the one of the upper disc plate and the lower disc plate; and a microprocessor that calculates a desired position of the upper disc plate relative to the lower disc plate and provides a control signal to each of the plurality of linear actuators to drive each of the plurality of linear actuators and move the upper disc plate and the lower disc plate to the desired positions.
 12. The electronically assisted artificial vertebral disc of claim 11, wherein the second sensor is a gyroscopic sensor coupled to the one of the upper disc plate and the lower disc plate.
 13. The electronically assisted artificial vertebral disc of claim 7, wherein the upper disc plate includes a plurality of first slots at positions circumferentially surrounding the ball and the trough, each of the plurality of first slots engaging the first universal joint of each of the plurality of linear actuators, and wherein the lower disc plate includes a plurality of second slots at positions circumferentially surrounding the ball and the trough, each of the plurality of second slots engaging the second universal joint of each of the plurality of linear actuators.
 14. The electronically assisted artificial vertebral disc of claim 13, wherein at least one of the plurality of first slots and the plurality of second slots is equally spaced around a perimeter of the ball and the trough.
 15. The electronically assisted artificial vertebral disc of claim 13, wherein the plurality of first slots includes three slots equally spaced around a perimeter of the ball and the trough, and wherein the plurality of second slots includes three slots equally spaced around the perimeter of the ball and the trough.
 16. The electronically assisted artificial vertebral disc of claim 13, wherein the trough includes a plurality of channels on a circumferential surface thereof, the circumferential surface extending in a direction away from the one of the upper disc plate and the lower disc plate, and wherein each of the plurality of channels corresponds to a slot of one of the plurality of first slots and the plurality of second slots.
 17. The electronically assisted artificial vertebral disc of claim 1, wherein the plurality of linear actuators includes three linear actuators equally spaced around a perimeter of the ball and the trough.
 18. The electronically assisted artificial vertebral disc of claim 1, wherein the control device includes: a plurality of first sensors, each of the plurality of first sensors coupled to one of the plurality of linear actuators and detecting a position of the one of the plurality of linear actuators; a second sensor coupled to one of the upper disc plate and the lower disc plate, the second sensor detecting a spatial orientation of the one of the upper disc plate and the lower disc plate; and a microprocessor that calculates a desired position of the upper disc plate relative to the lower disc plate and provides a control signal to each of the plurality of linear actuators to drive each of the plurality of linear actuators and move the upper disc plate and the lower disc plate to the desired positions.
 19. The electronically assisted artificial vertebral disc of claim 18, wherein the second sensor is a gyroscopic sensor coupled to the one of the upper disc plate and the lower disc plate.
 20. The electronically assisted artificial vertebral disc of claim 18, wherein each of the plurality of first sensors includes a sensor that detects a rotational position of a portion of each of the plurality of linear actuators.
 21. An electronically assisted artificial vertebral disc, comprising: an upper disc plate; a lower disc plate disposed beneath the upper disc plate; a mechanism that provides relative motion between the upper disc plate and the lower disc plate, an actuator for imparting movement to at least one of the upper disc plate and the lower disc plate; and a control device that continuously controls the actuator and an amount of movement between the upper disc plate and the lower disc plate, wherein the actuator includes a plurality of linear actuators interposing the upper disc plate and the lower disc plate, each of the linear actuators including a first end coupled to the upper disc plate and a second end coupled to the lower disc plate, and wherein the control device includes: a plurality of first sensors, each of the plurality of first sensors coupled to one of the plurality of linear actuators and detecting a position of the one of the plurality of linear actuators; a second sensor coupled to one of the upper disc plate and the lower disc plate, the second sensor detecting a spatial orientation of the one of the upper disc plate and the lower disc plate; and a microprocessor that calculates a desired position of the upper disc plate relative to the lower disc plate and provides a control signal to each of the plurality of linear actuators to drive each of the plurality of linear actuators and move the upper disc plate and the lower disc plate to the desired positions. 